The wafers being stored or transported are generally silicon wafers being processed into circuit chips. Wafers of other material such as gallium arsenide are also used for the same purpose. Other wafers are also processed and transported in this manner, such as memory disks, which may be metal with process coating on one side; and also glass substrates with process coatings. Wherever herein the word wafer is used, it is intended to include all of such types of wafers and disks and substrates.
In the storage and transport of such memory disks or wafers, there is always concern for the possibility of breakage and causing damage to the wafers because the wafers, as they are being processed, are quite valuable and breakage occurs relatively easily. The wafers may be on the order of 0.050 inches thickness and may be in the general size range of 48 millimeters diameter, 65 millimeters and larger. At least these smaller wafers are oftentimes contained in wafer carriers which have spacers in the sidewalls to space the wafers from each other; and such wafer carriers have open tops and open bottoms to accommodate processing liquids including rinsing water. Although such wafer carriers might in some instances be confined in a box or container with a cover, it is also convenient in some circumstances to simply apply a cover onto the top of the wafer carrier and onto the bottom of the wafer carrier to fully enclose the wafers for transport and storage. Such covers have been previously known as illustrated in U.S. Pat. No. 4,557,382.
It is important that the wafers remain fairly stationary within the wafer carrier for transport and storage, and accordingly, cushioning devices have been incorported into the cover as illustrated in the patent mentioned above. Such cushioning devices as the downwardly protruding fingers will generally rub along the edges of the wafers as the cover is applied, which tends to generate particles, causing contamination of the faces of the wafers with such particles.